That this (Alter Lankester, loc. cit.) in-sinking has taken place, and that the lung-books or in-sunken gill-books of Scorpio really represent appendages (that is to say, limbs or parapodia) is proved by their developmental history (see FIG.
In 1866 the Russian embryologist Kowalewsky startled the zoological world with a minute account of the developmental changes of Ascidia, one of the Tunicata, 5 and it became evident that the affinities of that class were with the Vertebrata, whilst their structural agreements with Mollusca were only superficial.
It is impracticable here to consider fully all the various developmental phases and modifications of the life-cycle described as occurring in the above parasites.
Some authors looking upon these as parthenogenetic ova regard the developmental cycle as one composed of an alternation of parthenogenetic and of sexual generations.
His most important memoirs, besides that just mentioned, are those on the anatomy and classification of Fishes, on the Caecilians and on the developmental history of the Echinoderms.
After the gastrula stage, which is found as a developmental stage in all Enterozoa, the embryo of the Hydrozoa proceeds to develop characters which are peculiar to the Coelen- a terata only.
The life-history of Schistostomum haematobium is still unknown, but the difficulty in obtaining developmental stages in any of the numerous intermediate hosts that have been tried suggests that the ciliated larvae may develop directly in man and either gain access to him by the use of impure water for drinking or may perforate his skin when bathing.
Loisy's developmental defence of Catholicism; Professor Harnack's review of L'Evangile et l'Eglise in the Theol.
Rhabditis nigrovenosa has a developmental history which is entirely anomalous, passing through two sexual generations which regularly alternate.
The sexual cells are borne on the mesenteries in positions irrespective of obvious developmental radii.